zen trace analysis support (#945)

Integrates the **tourist** trace analysis library and builds a full `zen trace` command suite for working with Unreal Engine `.utrace` files.

### Trace analysis library (`thirdparty/tourist/`)
- Adds the tourist library as a third-party dependency with three modules: **foundation** (platform primitives, memory, scheduling), **trace** (UE Trace protocol decoding), and **analysis** (event dispatching and analyzer framework).
- Cross-platform support for Windows, Linux, and macOS.

### `zen trace` CLI commands (`src/zen/cmds/`, `src/zen/trace/`)
- **`zen trace analyze`** — Summarize a `.utrace` file: session metadata, thread inventory, command line + build configuration, CPU profiling scopes, timing, event rates, log messages, and (with symbols) memory allocation metrics including live-allocs dumps, callstack-keyed aggregation, and allocation churn. Optional HTML output for memory reports.
- **`zen trace inspect`** — Dump the event schema (declared types, fields, sizes) from a trace file.
- **`zen trace trim`** — Extract a time-window from a trace into a new `.utrace` file.
- **`zen trace serve`** — Launch a local HTTP server hosting an interactive trace viewer; opens in the default browser.

### Symbolication (`src/zen/trace/symbol_resolver.*`, `thirdparty/raw_pdb/`)
- Pluggable resolver with multiple backends: `pdb` (in-tree raw_pdb), `dbghelp` (Windows), `llvm-symbolizer` (all platforms), `atos` (macOS). An `auto` backend picks the best available tool per platform.
- Microsoft Symbol Server support: downloads PDBs on demand using a redirect-aware HTTP client.
- Local PDB cache keyed by image GUID preserves symbols across binary recompilation.
- Callstack trimming heuristic strips UE internal noise from reports.
- Binary analysis cache (`.ucache_z`) avoids re-resolving the same trace.

### Interactive trace viewer (`src/zen/frontend/html/`, `src/zen/trace/trace_viewer_service.*`)
- Timeline: scope-level detail, horizontal zoom/pan, vertical scrolling, viewport-driven loading with pre-computed LOD for responsive navigation of large traces.
- Thread grouping (collapsible sidebar sections) synthesized from name suffixes, natural sort order, visual distinction between lane threads and OS threads.
- Bookmark and region annotations; region categories with per-category toggles; bookmark marker toggle in the toolbar.
- Filterable Logs tab showing captured `UE_LOG` output.
- Stats tab with per-scope aggregate statistics.
- Memory tab with interactive allocation analysis and an allocation size histogram.
- CsvProfiler event parsing and chart UI.

### Other in-branch supporting changes
- **Cross-platform browser launcher** (`browser_launcher.{h,cpp}`) used by `trace serve`.
- **`ReciprocalU64`** fast 64-bit integer division (zencore/intmath) for trace analyzers.
- **`parallelsort`** cross-platform parallel sort helper (zenutil).
- Frontend zip build rule so the viewer's HTML assets are bundled into `zen.exe`.
- `/Zo` flag for better optimized debug info on Windows release builds.
- `trace-tests.cpp` in the `zen-test` harness (harness itself landed on main via #985).

1 files changed, 148 insertions, 0 deletions

diff --git a/src/zenutil/parallelsort.cpp b/src/zenutil/parallelsort.cpp
new file mode 100644
index 000000000..8a9f547bc
--- /dev/null
+++ b/src/zenutil/parallelsort.cpp
@@ -0,0 +1,148 @@
+// Copyright Epic Games, Inc. All Rights Reserved.
+
+#include <zenutil/parallelsort.h>
+
+#include <zencore/testing.h>
+
+namespace zen {
+
+#if ZEN_WITH_TESTS
+
+void
+parallelsort_forcelink()
+{
+}
+
+TEST_SUITE_BEGIN("util.parallelsort");
+
+TEST_CASE("empty range")
+{
+	WorkerThreadPool   Pool(2);
+	eastl::vector<int> Vec;
+	ParallelSort(Pool, Vec.begin(), Vec.end(), [](int A, int B) { return A < B; });
+	CHECK(Vec.empty());
+}
+
+TEST_CASE("single element")
+{
+	WorkerThreadPool   Pool(2);
+	eastl::vector<int> Vec = {42};
+	ParallelSort(Pool, Vec.begin(), Vec.end(), [](int A, int B) { return A < B; });
+	CHECK(Vec.size() == 1);
+	CHECK(Vec[0] == 42);
+}
+
+TEST_CASE("small array below threshold")
+{
+	WorkerThreadPool   Pool(2);
+	eastl::vector<int> Vec = {5, 3, 8, 1, 9, 2, 7, 4, 6, 0};
+	ParallelSort(Pool, Vec.begin(), Vec.end(), [](int A, int B) { return A < B; });
+	for (size_t I = 0; I < Vec.size(); ++I)
+	{
+		CHECK(Vec[I] == int(I));
+	}
+}
+
+TEST_CASE("large array triggers parallel path")
+{
+	WorkerThreadPool Pool(4);
+
+	// 200K elements — well above the 64K threshold.
+	constexpr size_t		N = 200'000;
+	eastl::vector<uint32_t> Vec(N);
+
+	// Fill with descending values.
+	for (size_t I = 0; I < N; ++I)
+	{
+		Vec[I] = uint32_t(N - 1 - I);
+	}
+
+	ParallelSort(Pool, Vec.begin(), Vec.end(), [](uint32_t A, uint32_t B) { return A < B; });
+
+	for (size_t I = 0; I < N; ++I)
+	{
+		CHECK_MESSAGE(Vec[I] == uint32_t(I), "index=", I, " got=", Vec[I]);
+	}
+}
+
+TEST_CASE("already sorted")
+{
+	WorkerThreadPool Pool(4);
+
+	constexpr size_t		N = 200'000;
+	eastl::vector<uint32_t> Vec(N);
+	for (size_t I = 0; I < N; ++I)
+	{
+		Vec[I] = uint32_t(I);
+	}
+
+	ParallelSort(Pool, Vec.begin(), Vec.end(), [](uint32_t A, uint32_t B) { return A < B; });
+
+	for (size_t I = 0; I < N; ++I)
+	{
+		CHECK_MESSAGE(Vec[I] == uint32_t(I), "index=", I, " got=", Vec[I]);
+	}
+}
+
+TEST_CASE("reverse sorted")
+{
+	WorkerThreadPool Pool(4);
+
+	constexpr size_t		N = 200'000;
+	eastl::vector<uint32_t> Vec(N);
+	for (size_t I = 0; I < N; ++I)
+	{
+		Vec[I] = uint32_t(N - 1 - I);
+	}
+
+	ParallelSort(Pool, Vec.begin(), Vec.end(), [](uint32_t A, uint32_t B) { return A < B; });
+
+	for (size_t I = 0; I < N; ++I)
+	{
+		CHECK_MESSAGE(Vec[I] == uint32_t(I), "index=", I, " got=", Vec[I]);
+	}
+}
+
+TEST_CASE("duplicate keys")
+{
+	WorkerThreadPool Pool(4);
+
+	constexpr size_t		N = 200'000;
+	eastl::vector<uint32_t> Vec(N);
+	for (size_t I = 0; I < N; ++I)
+	{
+		Vec[I] = uint32_t(I % 100);	 // only 100 distinct values
+	}
+
+	ParallelSort(Pool, Vec.begin(), Vec.end(), [](uint32_t A, uint32_t B) { return A < B; });
+
+	for (size_t I = 1; I < N; ++I)
+	{
+		CHECK_MESSAGE(Vec[I - 1] <= Vec[I], "not sorted at index=", I);
+	}
+}
+
+TEST_CASE("custom comparator descending")
+{
+	WorkerThreadPool Pool(4);
+
+	constexpr size_t		N = 200'000;
+	eastl::vector<uint32_t> Vec(N);
+	for (size_t I = 0; I < N; ++I)
+	{
+		Vec[I] = uint32_t(I);
+	}
+
+	ParallelSort(Pool, Vec.begin(), Vec.end(), [](uint32_t A, uint32_t B) { return A > B; });
+
+	for (size_t I = 0; I < N; ++I)
+	{
+		CHECK_MESSAGE(Vec[I] == uint32_t(N - 1 - I), "index=", I, " got=", Vec[I]);
+	}
+}
+
+TEST_SUITE_END();
+
+#endif
+
+}  // namespace zen